As one of methods for pulling a single crystal from a crucible containing a melt of such semiconductor material as silicon, a Czochralski (CZ) method has been conventionally employed, which is schematically shown in FIG. 17. First of all, when a seed crystal 12 is brought into contact with a melt 10a within a crucible 10 installed in a heating chamber (not shown) and then pulled, moving-up operation of the seed crystal 12 at its pulling speed causes a neck part 13 to be formed in a lower part of the seed crystal 12. Then formed in a lower part of the neck part 13 is a single crystal part 15 (which is a combination of a cone-shaped part 15a and a straight body part 15b) which is dislocation free. Reference numeral 41 denotes a hanging member for pulling the seed crystal.
The single crystal part 15 has conventionally been as small as about 20-30 kg in weight and also small in diameter. In these years, however, for the purpose of increasing efficiency and yield in semiconductor production, the single crystal part 15 has been demanded to have an larger diameter and larger weight. For this reason, such a neck part 13 as shown in FIG. 17 has had a problem that it cannot safely support the single crystal part 15 as heavy as about 100-200 kg. In order to solve the problem, there have been employed a single crystal growing method and apparatus in which a corrugated portion 14 formed between the neck part 13 and single crystal part 15 is held as grasped by a pair of lifting jig 14a and pulled, as shown in, e.g., FIG. 18.
Well known techniques substantially similar to such a growing method as shown in FIG. 18 are disclosed, e.g., in Japanese Patent Application Laid-Open Publication Nos. 62-288191, 63-252991, 3-285893 and 3-295893, which have all different features. In Japanese Patent Application Laid-Open Publication No. 3-285893, for example, a seed crystal is first pulled by a wire connected to the seed crystal, a narrow part (corresponding to the corrugated portion 14 in the aforementioned example) as a pulled part formed following the seed crystal is grasped by a grasping lever (corresponding to the aforementioned lifting jig 14a) located at a predetermined position, and then the single crystal is further pulled by the wire and lever.
The neck part 13 shown in FIG. 17 generally has a diameter of about 3-4 mm and has a strength insufficient to pull the heavy-weight single crystal part 15. To avoid this problem, there is disclosed in Japanese Patent Application Laid-Open Publication No. 5-43379 a technique in which pulling conditions are devised so that the neck part 13 can have a diameter of 4.5 mm-10 mm. However, this method is insufficient to form the single crystal part 15 safely and without generation of dislocation.
Methods for solving the above problem includes the techniques shown in FIG. 18 and disclosed in the aforementioned Publications. However, these prior arts have problems which follow. First, in order to form the aforementioned corrugated portion 14, it is necessary to adjust the pulling rate or speed of the seed crystal 12 and the temperature of the melt within the crucible, and it is per se difficult to form the corrugated portion 14 in a desired shape at a fixed position.
For this reason, it is preferable that the single crystal can be held by a raised and recessed portion (verge: Journal of Crystal Growth 52(1981)391-395) in a neck part formed to cause dislocation to disappear from the single crystal or by a part of finely fluctuated diameters caused during the growth of the single crystal.
Thus, when the lifting jig 14a having a constant arm length is installed at a fixed position as in the above known technique, an engagement position between the lifting jig 14a and corrugated portion 14 is not stable, which tends to involve such a problem that the engagement becomes insufficient. Further, the lifting jig 14a and its holding portion are positioned relatively in the vicinity of the crucible 10 at a high temperature as shown in FIG. 18, which requires the jig to be made of special material, which leads to the fact that the jig becomes expensive and the member material thereof may become a cause of contamination in the melt of the crucible 10.
The biggest problem is that it is difficult to engage the lifting jig 14a with the corrugated portion 14 or with the single crystal part 15 being pulled as rotated under a condition of no impact force. Even a slight impact force applied to the single crystal part 15 during the formation of the single crystal part 15 results in generation of dislocation in the crystal. Accordingly, in order to form a good quality of single crystal part 15, it is necessary to engage the lifting jig 14a under a condition of no impact force. However, no consideration is paid to this respect in the aforementioned prior arts.
It is therefore an object of the present invention to provide a single crystal growing method and apparatus which can solve the above problems in the prior art, can realize safe and reliable pulling operation of a heavy-weight single crystal, can minimize an impact force caused when a crystal is held, and can reliably prevent the generation of dislocation in the crystal.